A. Conventional X-ray Contrast Agents
An x-ray contrast agent is administered for the purpose of visualizing physiological structures or functions with x-rays or computer tomography (CT). X-ray contrast agents may be comprised of complex molecules containing electron dense labels. Conventional x-ray contrast agents in general use are composed of iodine, which provides opacification to the x-rays, which is attached to an aromatic nucleus, which provides a high degree of stability required for pharmacological inertness. This basic aryl iodide unit may be modified by various chemical groups in order to provide the necessary high water solubility, in vivo stability, selective excretion and low viscosity and to minimize adverse side effects, such as osmotic or cytotoxic side effects.
Conventional x-ray contrast agents may include intravascular or targeted contrast agents. Intravascular agents are currently widely used and are non-selective. The few targeted x-ray contrast agents currently known are predominantly designed for targeting the fixed macrophages of the reticuloendothelial system (RES), in particular, the Kupffer cells for liver imaging.